Hi, We're currently @our tournament and we have encountered this issue again...
I did not find any correct answer, so that's why I'm asking again:

A model is engaged with the Feral Hammerfist and with a brute.
When the brute leaves the melee range of the engaged model :
- does it get hit by a free strike?
- Does the engaged model fully loose the free strike
- or can the free strike been made against the Hammerfist???

Seems the question was more or less lost in the discussion and needs to be cleared in the FAQ/errata.
In my understanding, I would go with the second interpretation in which the model looses the free strike by a combination of two rules:
- the model may not attack the disengaging model because of Threaten (not even with free strikes).
- the model may not make a free strike against the Hammerfist as the Hammerfist does not provoke any free strike.

I was on the receiving end of this Hammerfist model (which I then smashed the turn thereafter, tell them the whole story Laurens ) In the end there was no need for any free strike as the Brute did not leave combat.

Yet I must say that I do not agree with the fact that the free strike is lost, free strike is a penalty one takes for disengaging quite unorderly (they just turn their back and run). Even when looking through the eyes of the model, I can't see why one would not take this opportune chance to dispose of a foe, even if there's something threatening next to you. You can basically just do some penaltyless disengaging shenanigans and maybe even line for a new charge next round. I know my word counts for a lot less, but I felt I just had to state my disagreement. I'll adhere to the ruling made though.

I also think rule 2 looks like the right one, but there should indeed be a FAQ to this.

The combo of the Hammerfist and loosing all free strikes is cruel...
Maybe an extra rule for Threaten like: When making free strikes against models other then the Hammerfist, reduce the final POW by D3/D6...

Interpretation 2 is right and as it was intended. Think of it as a big bad angry beast (I guess none has a problem to imagine that...) so threatening that it allows his fellows to fall back. The enemies are just so intmidated by his sheer brute force that they hesitate and miss the short moment where there is an opening in their opponents defense to make a free strike.

But remember that only the enemies that are engaged by the hammerfist lose their free strikes...